103CIPHER

Encrypting a message by multiplying it by a matrix, and decrypting it by inverting that matrix.

A first contact with cryptography, through mathematics rather than computing: the message is turned into numbers through the ASCII table, split into blocks, then multiplied by a key matrix built the same way. Decrypting it would require inverting that matrix — and discovering that not every matrix is invertible, which limits the usable keys. The deliverable covers encryption; inversion remained the project's extension.

Encrypting a message through a matrix product: key and message converted to ASCII codes, laid out in the smallest possible square matrix and in a matrix with as many columns, then multiplied.